Issue 58

W. Frenelus et alii, Frattura ed Integrità Strutturale, 58 (2021) 128-150; DOI: 10.3221/IGF-ESIS.58.10

Long-term degradation, damage and fracture in deep rock tunnels: A review on the effect of excavation methods Wadslin Frenelus, Hui Peng, Jingyu Zhang Department of Hydraulic Engineering, College of Hydraulic and Environmental Engineering, China Three Gorges University, Yichang 443002, China wadslin@ctgu.edu.cn, https://orcid.org/0000-0002-9084-2548 406955991@qq.com, 304428211@qq.com

A BSTRACT . Rocks are frequently host materials for underground structures, particularly for deep Tunnels. Their behavior plays a fundamental role in the overall stability of these structures. In fact, the erection of deep tunnels imposes rocks excavations around the defined routes. These excavations are generally carried out by various methods of which the most used are Drill- and-Blast (DB) and Tunnel Boring Machine (TBM). However, regardless of the tunnelling method used, the impacts such as the perturbation of the initial stress field in rocks and the release of the stored energy are always significant. The impacts produce damage, fractures and deformations which are generally time-dependent and influence the long-term stability of deep tunnels built in rocks. Thus, by considering the aforementioned excavation methods, this paper identifies, reviews and describes the relevant factors generated during and after rock excavations. Interestingly, such factors directly or indirectly influence the long-term stability and therefore the structural integrity of deep rock tunnels. In addition, some recommendations and proposals for future works are presented. This paper can provide useful references in understanding the degradations, damage and fractures generated by tunnelling methods and facilitate suitable actions to ensure long-term stability of deep underground structures. K EYWORDS . Excavation methods; Excavation impacts; Rocks behavior; Deep Tunnels; Structural Integrity; Long-term Stability.

Citation: Frenelus, W., Peng, H., Zhang, J., Long-Term Degradation, Damage and Fracture in Deep Rock Tunnels: A review on the effects of Excavation Methods, Frattura ed Integrità Strutturale, 58 (2021) 128-150.

Received: 13.05.2021 Accepted: 03.08.2021 Published: 01.10.2021

Copyright: © 2021 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

I NTRODUCTION

espite many challenges generally encountered in underground excavations, engineering projects for the construction of deep tunnels continue to grow. Indeed, the underground space needs are necessary from day to day particularly in developed countries. It is thereby widely known that deep tunnels can be built for various purposes such as water conveyance, reservoirs emptying, hydropower stations, sanitary drainage, etc. As a result, the long- term stability of these tunnels must be guaranteed, so that they can perform their roles correctly throughout their period of operation. However, this long-term stability is influenced by many potential factors, including the methods used to excavate these tunnels. D

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